health: build the instrumentation only when asked for

The counters, the phase hooks in idle() and the "health" command are now
behind HEALTH, set from the command line with HEALTH=1. Without it the
hooks are empty macros and the command does not exist, so a default build
carries none of it: on SWTGW218AS that is 1065 bytes of bank 2, 101 of the
common segment and 28 of xdata, plus seven banked calls per main-loop pass.

It is a developer's tool. Reading the dump takes knowing the main loop, and
a user who needs it for a report can build with the flag on, which is how
the kernel treats its lock and latency instrumentation as well.

cmd_parser.h

@@ -9,7 +9,10 @@ extern __xdata uint8_t cmd_buffer[CMD_BUF_SIZE];
 extern __xdata uint8_t cmd_available;
 extern __xdata uint8_t err_status;
 
-/* Phase ids of the health instrumentation, in main-loop order */
+/* Health instrumentation, built with HEALTH=1. Without it the hooks below
+ * compile to nothing and the "health" command does not exist. */
+#ifdef HEALTH
+/* Phase ids, in main-loop order */
 #define HEALTH_PH_LINK	0
 #define HEALTH_PH_SFP	1
 #define HEALTH_PH_RX	2
@@ -19,11 +22,18 @@ extern __xdata uint8_t err_status;
 #define HEALTH_PHASES	6
 
 extern __xdata uint16_t health_rx_frames;
+#define health_rx_frame()	health_rx_frames++
 
 void health_loop_start(void) __banked;	/* once per idle() pass, resets the phase baseline */
 void health_phase(uint8_t id) __banked;	/* after each phase; accounts ticks since last checkpoint */
 void health_stack_paint(void) __banked;	/* paint the unused stack area once at boot */
 void health_show(void) __banked;	/* "health" CLI dump */
+#else
+#define health_rx_frame()
+#define health_loop_start()
+#define health_phase(id)
+#define health_stack_paint()
+#endif
 
 void cmd_tokenize(void) __banked;
 void cmd_parser(void) __banked;